1. Field of the Invention
The invention relates to magnetic spin based photonic/plasmonic devices. In particular the present invention is related to modulation via a magnetic field of electromagnetic signals in photonic/plasmonic devices that may partially comprise a ferromagnetic material which may be a layer exhibiting a spin-dependent permittivity, permeability or electron transport.
2. Description of the Related Technology
With the growing demand for high-speed, high bandwidth information technology, there has been increasing interest in the use of photonic devices to carry and control information signals. Modulators, switches, and filters are key components of any information-based technology. The development of photonics devices, with these functionalities and based on the application of external electric fields or acoustic signals, has been well established. However, there has been relatively little attention paid to modulation, switching, and filtering schemes based on the application of a magnetic field, apart from a small class of magneto-optic devices.
Surface plasmon waves are waves that propagate along the surface of a conductor, wherein the conductor is usually a metal. Surface plasmon waves offer a way to channel light on a chip using sub-wavelength structures. Miniaturized circuits can convert light into a surface plasmon, which can then be propagated and processed by logic elements located on the circuit before being converted back into light. The circuitry used to propagate surface plasmon waves may also be used to carry electrical signals or may be integrated with separate digital electronic circuits.
A new branch of photonics that uses surface plasmon waves is called plasmonics. Plasmonic circuits may have basic component functionality, including waveguides, switches and tuners, W. L Barnes et al, Nature, vol. 424, 824 (2003), S. A Maier et al., Nature Materials, vol. 2, 229 (2003), and S. A. Maier et al., Advanced Materials, vol. 13, 1501 (2001) and N. Engheta et al. “Circuit elements at optical frequencies: nano-inductors, nano-capacitors, and nano-resistors”, Phys. Rev. Lett. 95, 095504 (2005). One of the major challenges in active plasmonic and nanoplasmonics devices is the ability to directly control the coherent plasmon oscillations via external stimulus. This stems from the fact that direct manipulation of the electron density distribution within the metal's conduction band is necessary for such a purpose. However, unlike carriers in semiconductors, in metals the free electron density is very high and the Fermi level is located high within the conduction band. Thus, external modulation of the density of state is very challenging in achieving any tangible modulation on the metal's optical properties. Effectively, directly modulating the density of the state of the electrons in the conduction band is notably insignificant on the characteristic conductivity, amplitude, phase, and plasmons oscillating frequency. One way to achieve these functionalities is via the manipulation of the electron spin state. Spintronic devices that exploit electron spin rather than the charge enable nano-scale logic devices with enhanced functionality and lower power consumption. M. Johnson, I.E.E.E. Spectrum vol. 37 (2), 33 (2000); U.S. Pat. No. 6,804,146; U.S. Pat. No. 6,809,959; U.S. Pat. No. 7,050,329; and U.S. Pat. No. 7,068,535.
However, the advantages of both spintronic and plasmonic technologies have not been fully realized. Therefore there is a need in the field to combine the advantages of both spintronic and plasmonic technologies in order to obtain low power, functionally diverse photonic/plasmonic devices.